Rosin size emulsion



Patented June 2, 1942 UNITED STATES PATENT OFFICE ROSIN SIZE EMULSIONEdmund A. Georgi and Arthur L. Osterhof, Wilmington, Del., assignors toHercules Powder Company, Wilmington, Del., a corporation of Delaware NoDrawing. Application September 16,1940, Serial No. 357,007

.precipitated on the stock fibres by means of alum or other suitableprecipitant. Such saponified rosin size emulsions are in generalprepared by reacting gum or wood rosin with an alkali, such as sodiumhydroxide or sodium carbonate,

whereby at least a part of the abietic and other salt during storage orupon dilution. Other objects will be apparent from the followingdetailed description of the invention.

1 have found that the above objects may be attained in rosin sizeemulsions prepared from wood rosin which has been subjected toheattreatment at temperatures below its decomposition temperature. besufiicient to reduce substantially the tendency for the rosin to deposit3:1 salt upon subsequent saponiflcation, but should not be suflicient todestroy the crystallizability of the rosin, since heat-treatment to suchan extent causes the rosin acids present in the rosin are converted into4 their water-soluble alkali-metal salts, and thereafter forming adilute emulsion of the reaction product in water. Emulsification isreadily effected since the alkali-metal resinates act as emulsifyingagents for the unsaponified portion of the rosin. I

Although rosin size emulsions prepared in this manner are widely used inthe paper-sizing art, they possess several serious disadvantages, amongwhich is a tendency to induce frothing or foaming of the sized stockduring the subsequent paper-forming operations. Foam not only interfereswith the proper operation of the papermaking machine by accumulating onthe screens and in the head boxes and by carrying considerablequantities of fibre, filling material and size into the waste, but alsoresults in the formation of inferior paper having characteristic surfaceimperfections known as froth spots.

The prior art rosin size emulsions, particularly those containing alarge proportion of free rosin as a result of being prepared from onlypartially saponified wood rosin, have the further disad-' vantage oftending to deposit a crystalline product upon standing. This crystallineproduct is known in the art as 3:1 salt" and is a double salt consistingof three molecules of abietic acid and one molecule of an alkali-metalabietate. During the paper-making process it collects as a sludge in thedilution and storage tanks and constitutes a source of greatinconvenience to the paper-maker.

It is accordingly an object of this invention to provide rosin sizeemulsions which do not induce frothing or foaming during paper-makingoperations. Another object is to provide rosin size emulsions which donot deposit a sludge of 3:1

formation of considerable amounts of rosin oils. The presence of suchoils is undesirable in the size since they are not readily emulsifiedand are lacking in sizing value, contain corrosive constituents, and maybecome the cause ofsurface imperfections on the paper web. The sizeemulsions prepared according to the invention,- how-. ever, contain onlyvery smallamounts of the undesirable rosin oils and at the same time aresubstantially free from 3:1 salt formation and foaming duringpapermaking operations. They are further advantageous in that they haveunusual stability without the use of protective colloids, even whencontaining as high as 40 per cent of free rosin. a

As hereinbefore mentioned, the new and im-- proved size emulsionsprovided by the present invention are prepared from wood rosin which hasbeen heat-treated to an extent sufficient to effect a substantialreduction in the tendency of its saponlflcation product to form 3:1 saltbut insufllcient to destroy its crystallizability. Such heat-treatmentmay be carried out batch-wise simply by heating wood rosin, which haspreferably but not necessarily been color-refined, for

example, by selective solvent extraction, at a temperature below itsdecomposition temperature, e. g. between about 250 C. and about 350 C.

and preferably under non-oxidizing conditions,

' until the desired change in the rosin has taken place.

More'pneferably, however, the heat-treatment is carried out continuouslyas described in detail in the co-pending application of Henry A.Johnstone, Serial No. 356,958, filed September 16, 1940. I

. Such method consists essentially in'passing the Such heat-treatmentshould the required length of time. The reaction vessel is vented toprovide exit for any gaseous or highly volatile products which may beformed, but it will be noted that the heating is carried out in suchmanner that substantially no distillation of the rosin takes place.

The time required to effect the desired changes in the rosin varies withthe temperature at which the heat-treatment is carried out as well aswith the particular type and grade of rosin employed. Ordinarily,however, it will be found that from minutes treatment at 350 C. to about5 hours treatment at 250 C. will be satisfactory. The extent of theheat-treatment may also be measured by determining the specific rotationof the rosin. Rosin which has been heat-treated until its specificrotation in the solid state has been raised from a negative value to avalue above about +5 is substantially free from 3:1 salt formation,whereas rosin which has been heat-treated until its specific rotationhas been raised to above +20 will have lost its crystallizability andwill contain an undesirable proportion of rosin oils. Accordingly, therosins which are suitable for use according to the invention are thosewhose specific rotation as determined in the solid state has beenincreased to a value between about +5 and +20, preferably between aboutand about by heating at temperatures between about 250 C. and 350 C. k

The heat-treatedrosin is then saponifled by adding it in the solid ormolten state to a hot aqueous solution of an alkali, such as sodiumcarbonate, potassium hydroxide, ammonia, sodium hydroxide, etc., andheating the mixture until the reaction is complete. The concentration ofthe aqueous alkali solution is usually so adjusted that upon completionof the reaction suflicient water is present to form a paste size ofdeperature of about 80 C. and thereafter further diluting to the desiredconcentration and quickly chilling by admixture with cold water. If desired, stabilizing agents, such as proteins, watersoluble gums, etc.,may be incorporated into the size emulsion, although the use of suchagents is not required.

The following example illustrates one way in which the principle of theinvention has been applied but is not to be construed aslimiting thesame:

Two hundred and seventy pounds of K wood rosin was placed in a stainlesssteel kettle and heated at a temperature of about 300 C. for 30 l5-minutes, after which it was cooled as quickly as possible by sprayingwater on the sides of the kettle. After cooling it was found that thespecific rotation of the rosin in the solid'state had been raised to a.value of about +10.4 by the heat-treatment but that the rosin wasreadily crystallizable. One hundred pounds of this material was thensaponifled by mixing with 59 sired consistency and solids content. Theproportion of alkali employed varies with the par-' ticular alkali aswell as with the type of size desired. In preparing neutral sizes, forexample, suflicient alkali is employed to react with all of thesaponifiables in the rosin, whereas in preparing high free rosin sizeswherein the rosin is only partially saponified a smaller quantity ofalkali is used, the exact proportion depending upon the proportion offree rosin desired in the size. The saponification may. also be carriedout inthe cold, employing a variety of alkalies and special proceduresadapted to modify certain characteristics of the size. For example, itmay be carried out as described in U. S. Patent No. 2,134,911, wherebythe size is spray-dried to form a dry finely-divided powder. Othervaripounds of hot 22 per cent by weight aqueous sodium carbonate andheating at a temperature of about 85 C. for about 40 minutes. The rosinsize so prepared was a thick paste containing about '79 per cent byweight solids, 19 per cent by weight of which was free rosin asdetermined by titration. This material was then emulsified to form anaqueous emulsion containing 3 per cent by weight solids by the gradualdilution method, 1. e. by diluting it with approximately 5.8 parts byweight of water at a temperature of about 80. C. and thereafter mixingthe diluted size with about 3.5 parts by weight thereof of hot waterwith violent agitation. The emulsion so prepared was stable and did notprecipitate 3:1 salt upon storage over long periods of time at elevatedtemperatures.

The tendency of the emulsion to form 3:1 salt was estimated quantitivelybydissolving a 50 gram sample of the heat-treated rosin from which ithad been prepared in 50 grams of warm ations will readily occur to thoseskilled in the art.

The dilution of the saponifled heat-treated 6o rosin to form the sizeemulsion may be carried out in a number of ways, the simplest of whichconsists merely in adding the thick size to hot water with violenta-gitation.- The emulsion may also be formed by the so-called gradualdilution method which consists in thinning the size to about a 15-percent solids content with hot water and then adding the diluted sizeto acetone, and thereafter adding sufficient dilute aqueous sodiumhydroxide to neutralize onefourth of the acids present in the rosin. Theacetone solution was allowed to cool to room temperature and was seededwith a crystal of 3:1 salt. After standing for 24 hours the solution wasfiltered and the residue weighed, whereby there was obtained a 0.10 percent yield of 3: 1 salt. Wood rosin which had not been heattreatedyielded 29.4 per cent by weight of 3:1 salt when tested by this method.

A similar emulsion was prepared by diluting the paste size to 16. percent concentration with distilled water at a temperature of-"?v C. andthereafter further diluting to 3 per cent concentratibn at C. Theemulsion was then cooled and tested directly for 3:1 salt formation bystoring in an oven maintained at 75 C.

After 24 hours storage, the emulsion had acquired only a very faintturbidity, whereas similar size emulsions prepared from rosin which hasnot been heat-treated thicken andbecome completely opaque when tested inthismanner.

The follow table presents data obtained by subjecting several typicalrosin size emulsions prepared in a manner similar to that describedabove to a standard foam test under conditions simulating thoseencountered during paper-sizing. Comparative data are also included onsimilar rosin size emulsions prepared from rosin which had not beenheat-treated as well as on a typical commercial size. The foaming testwas carried out. by diluting l milliliters of the3 per cent aqueous sizeemulsion with 500 milliliters of water and thereafter adding per centaqueous aluminum sulfate until the diluted emulsion had a pH of about4.5. The mixture was then placed in a foam-testing apparatus whichconsists of a cylindrical glass vessel having a co-axially mountedhollow metal tube running to the bottom thereof. Within the tube ismounted a shaft carrying a propeller at its lower end. When the mixtureis placed in the cylinder and the propeller rotated athigh speed, air issucked in through the hollow tube and is violently agitated with themixture, thereby causing foaming. The height to which the foam rises inthe vessel is read by means of graduations on the side of the vessel,each one-tenth inch of foam being considered as one foam unit.

Table Size composition Expqeriment Foam o. unit Free Rosin Solids rosinl Percent Percent 1 Heat-treated.-. 70. 2 l8. 2 2- o 69.2 26.1 3- do59.8 16l7 4. Not heat-treated. 70. 0 19. 0 5 d0 71. 2 21 8 6 Commercialsize 69. 8 20. 0

C. and about 350 C. for I from about 5 minutes to about 5 hours, saidheattreatment being suflicient toreduce substantially the tendency ofthe rosin to form 3:1 salt upon subsequent saponification butinsufiicient to destroy its crystallizability.

2. A dilute aqueous emulsion of a rosin size prepared by at leastpartially s'aponifying wood rosin whose specific rotation in the solidstate has been raised to a value between about '+5 and about +20 as theresult of having been heated at a temperature between about 250 C. andabout 350 0. forfrom about 5 minutes to about 5 hours, said heattreatment being suflicient to reduce substantially the tendency of therosin to form 32-1 salt upon subsequent saponification but insufiicientto destroy its crystallizability. 3. A' dilute aqueous emulsion of arosin size prepared by at least partially saponifying wood rosin whosespecific rotation in the solid state has been raised to a value betweenabout +10 and about +15 as the result of having been heated at atemperature between about 280 C. and about 325 C. for from about 5minutes to about 5 hours, said heat treatment being suflicient to reducesubstantially the tendency of the rosin to form 3:1 salt upon subsequentsaponification but insuflicient to destroy its crystallizability.

4. A dilute aqueous emulsion of a rosin size prepared by at leastpartially saponifying wood rosin which has been heat-treated at atemperature between about 250 C. and about 350 C. for from about 5minutes to about 5 hours to an extent suflicient to reduce substantiallyits tendency to form 3:1 salt upon subsequent saponification butinsuflicient to destroy its crystallizability,

said saponification being efiected by means of an aqueous alkaliselected from the group consisting of sodium hydroxide and sodiumcarbonate.

EDMUND A. GEQRGI. ARTHUR L. OS'I'ERHOF.

